Referential transparency

Property of a computer software expression or subroutine that replacing it in the code with its evaluated result does not change the program's behavior

In analytic philosophy and computer science, referential transparency and referential opacity are properties of linguistic constructions, and by extension of languages. A linguistic construction is called referentially transparent when for any expression built from it, replacing a subexpression with another one that denotes the same value does not change the value of the expression.